The present invention relates to a device that restricts frame oscillation to near zero degrees in articulated steerable mobile vehicles, for example low height underground mining vehicles such as coal scoops and other haulage vehicles. It relates particularly to a locking device to increase the stability, safety and resulting overhung load capacity of a three-point articulated machine. A problem arises when an operator of such machine attempts to carry extremely heavy loads outside of the wheel-base of the machine and where the two main parts of the machine, a front frame part and a rear frame part, are at a substantial articulated angle with respect to each other. When loading heavy equipment on the front of the front frame, the rear frame becomes less and less an effective counterbalance to oscillation (and tipping) as the steering angle between the frames increase. This, results in possible instability by reason of a rear wheel raising above the ground. Traction is lost and the machine becomes difficult to maneuver.